NASA TECHNICAL

MEMORANDUM

r-.tnCMI

x

NASA TM X-2574

CA LE^g^# &^^*-COPY

DESIGN AND PERFORMANCE EVALUATION

OF A CRYOGENIC CONDENSER

FOR AN IN-PILE EXPERIMENT

by Robert W, Graham, Richard J, Crum

and Yih-Ynn ffr//

Lewis Research Center

Cleveland, Ohio 44135

NATIONAL A E R O N A U T I C S AND S P A C E ADMINISTRATION • WASHINGTON, D. C. • JUNE 1972

1. Report No.

NASA TM X-25742. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

DESIGN AND PERFORMANCE EVALUATION OF A CRYOGENICCONDENSER FOR AN IN-PILE EXPERIMENT

5. Report DateJune 1972

6. Performing Organization Code

7. Author(s)

Robert W. Graham, Richard J. Crum, and Yih-Yun Hsu8. Performing Organization Report No.

E-6868

9. Performing Organization Name and Address

Lewis Research CenterNational Aeronautics and Space AdministrationCleveland, Ohio 44135

10. Work Unit No.

111-05

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

National Aeronautics and Space AdministrationWashington, D. C. 20546

13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

An apparatus was designed to enable in-pile irradiation of materials in liquid hydrogen atcryogenic temperatures. One of the principal components of this apparatus was a horizontaltube condenser. The performance of the condenser was evaluated by running a liquid-nitrogenprototype of the apparatus at heat loads comparable to or greater than those expected duringthe irradiation. The tests showed that the condenser was capable of handling the design heatload and that the design procedure was sound.

17. Key Words (Suggested by Author(s))

Cryogenic condenserCondenserLiquid nitrogen

18. Distribution Statement

Unclassified - unlimited

19. Security Classif. (of this report)

Unclassified20. Security Classif. (of this page)

Unclassified21. No. of Pages

11

22. Price'

$3.00

* For sale by the National Technical Information Service, Springfield, Virginia 22151

DESIGN AND PERFORMANCE EVALUATION OF A CRYOGENIC CONDENSER

FOR AN IN-PILE EXPERIMENT

by Robert W. Graham, Richard J. Crum, and Yih-Yun Hsu ' :

Lewis Research Center

' . . . ' . ' ' ' SUMMARY

. - ' . - ' " ' ' - • ' : '

An apparatus was designed to enable in-pile irradiation of materials in liquid hydro-gen at cryogenic temperatures. One of the principal components of this apparatus wasa horizontal tube condenser. The performance of the condenser was evaluated by run-ning a liquid-nitrogen prototype of the apparatus at heat loads comparable to or greaterthan those expected during the irradiation. The tests showed that the condenser wascapable of handling the design heat load and that the design procedure was sound.

.INTRODUCTION ;

As the result of a proposal to do some material studies in pile in liquid hydrogen,the design of a hermetically sealed test chamber suitable for insertion in the Plum BrookReactor was inaugurated. One of the design criteria to maximize safety of operation wasthat the hydrogen coolant be confined in a welded, lead-free test chamber and recycled;consequently, a.condenser was selected to be a major constituent of the apparatus.

A survey of the design literature revealed that there was practically no informationrelative to hydrogen condensing. What little was found pertained to vertical condensertubes, and the design of concern would have to involve horizontal tubes.

i.' ' ' ' . . , ' ' ' '

Of course, there is considerable literature pertaining to condensers in general -primarily those involving steam. Cpndensing-heat-transfer correlations do exist, buttheir applicability to an.entirely different thermal domain must be questioned. As ameans of evaluating the design procedure for hydrogen, it was considered advisable, todesign and test a nitrogen condenser prototype similar to the hydrogen one. Runningthis nitrogen prototype condenser out of pile would yield valuable information about theapplicability of the correlations and scaling laws employed. This report contains anevaluation of the nitrogen condenser performance with reference to its design. These

tests with the nitrogen condenser indicate that the design equations and procedure can beapplied to the hydrogen condenser with considerable confidence and the desired perform-ance of the condenser will be achieved.

APPARATUS AND PROCEDURE

Figure 1 shows the design concept of the apparatus as it was envisioned for theactual in-pile experiments where liquid hydrogen was the coolant. The material speci-mens to be tested would be placed in the liquid-hydrogen sump shown at the left side ofthe drawing. The nominal liquid-hydrogen temperature in the sump is 30 K (54° R).The condenser part of the apparatus comprises 15 horizontal tubes in which helium flowsas a coolant. The helium is to enter the condenser tubes at 24 K (43° R). The antici-pated heat load to be dissipated by the condenser is approximately 845 watts (2880Btu/hr). This heat load is the estimated gamma and neutron heating that will be devel-oped in the test hole of the reactor.

In carrying out the nitrogen prototype test program, electrical heaters were in-stalled in the heat exchanger to simulate the gamma and neutron heating that would beexperienced in pile. Sufficient electrical heating capacity was installed in the nitrogenheat exchanger to far exceed the anticipated design level. Since liquid nitrogen was tobe used as the coolant in the prototype heat exchanger instead of gaseous helium, thedesign-point heat flux for the prototype should be higher than that of the actual in-pileheat exchanger. The higher density and Prandtl number of the liquid nitrogen wouldeffect a greater transport of heat for comparable temperature differences and flow ve-locities. A number of ways of establishing this prototype heat load could be used.Through simulitude relations, one could compute the heat load on the condensing sideand on the coolant side for various conditions. It was decided that the most conserva-tive estimation would be to operate the nitrogen prototype at the same value of the flood-ing parameter

Exchanger

PrototypeHydrogen

Coolant tem-perature,

K

8023.8

Wall tem-perature,

K

9424.8

Estimated coolant-side heat-transfer

coefficient,W/(m2)(K)

30601300

Figure 2 shows the apparatus and how it was instrumented for the nitrogen experi-mental program. A liquid-level indicator was installed in the sump to give an approxi-mate idea of the amount of liquid nitrogen there. The instrument consisted of six carbonresistor circuits located at different positions on the probe. The sump was utilized asa convenient reference temperature bath for the cold junctions of the thermocouple in-strumentation.

The thermal conditions of the condenser coolant (liquid nitrogen) were determinedfrom platinum resistor bulk temperature measurements as the coolant entered the con-denser and when it discharged. A turbine-type flowmeter was used to monitor the flowrate. The liquid nitrogen pressures at the inlet and exit were measured.

As is shown in figure 2, one of the condenser tubes was instrumented with severaltypes of thermocouple sensors. The temperature difference AT between the outsidewall and the vapor surrounding the tube was measured at three axial stations, 14. 7,36. 8, and 61. 5 centimeters (5. 8, 14. 5, and 23. 2 in.) from the inlet. Centerline ATthermocouples were installed at four internal stations of the condenser tube. As shownin figure 2 they were located at 14. 7, 29. 4, 44. 2, and 58. 8 centimeters (5. 8, 11. 6,17. 4, and 23. 2 in.) from the inlet.

During the course of the test program, some of these thermocouples shorted oropened up and could not be repaired. Thus, not all of the instrument stations of the con-denser tube were available during the testing. However, a sufficient number remainedintact to yield performance information.

HEAT-TRANSFER DESIGN CALCULATIONS

The correlations and important assumptions pertinent to the design of the hydrogenapparatus and the nitrogen prototype are outlined in this section. Most of these corre-lations, when taken from their original references, were designated for use with U. S.customary units. They will be cited in their original published form. In cases wherethe predictions are dimensional, the conversion factors necessary to list them in SI unitsare presented.

Heat-Transfer Coefficient Inside Condenser Tubes

Hydrogen apparatus. - In the hydrogen apparatus, cold helium gas was to be used asthe condenser coolant. A simple, forced-convection correlation for gases obtained fromreference 1 was employed in estimating the inside-tube heat-transfer coefficients:

h = KG°-8d-°-2V-^ (Dw

where

h heat-transfer coefficient, Btu/(ft2)(hr)(°F); to convert to W/(m2)(K) multiply .by 5. 69

K proportionality constant which includes fluid properties as well as Dittus-Boelterconstant, c(k°' 6Cp' 4/M°' 4); K = 0. 020 for helium

G flow per unit area

d diameter or hydraulic diameter

Nitrogen prototype. - Liquid nitrogen was employed as the condenser coolant. Aconventional forced-convection correlation for liquids was utilized, namely,

' ' h = * CRe0' 8Pr°-25 (la)d

where Re is the Reynolds number, Pr is the Prandtl number, and C is a coefficient.

Condensing Heat-Transfer Coefficient Outside Tubes

Jakob (ref. 2, p. 673) suggests the following correlation for condensation with mul-tiple,horizontal tubes:

*/ 2 3= 0.725V P Xk g

V nMd(tf - th = 0. 725't/ P AK g (2)

where .

h heat-transfer coefficient, Btu/(hr)(ft2)(°F); convert to W/(m2)(K) by multiplyingb y 5.69 ' . - . • • • • • ;

p density, lbm/ft3

4

A heat of vaporization, Btu/lb .- . : ..

k thermal conductivity, Btu/(ft)(hr)(°F) ' •2

g gravity, ft/sec

n number of tubes • --. . •' /•

p. viscosity, lb/(ft)(hr)

d tube diameter, ft

to .saturation temperature,. °F . , . . . . ; . : . . . -

t surface temperature, °Fo

; ' ' • - • - . / •

' l Flooding or Holdup Estimation

Perhaps the most critical and questionable estimation in the entire design proce- 'dure is the one pertaining to the prediction of possible "flooding" in the condenser. By"flooding" we mean that the condensate is inhibited from returning to the sump by themoving vapor. A flobding criterion expressly developed for vertical condenser tubeswas used (ref. 3). No criterion for horizontal tubes was found in the literature. Theflooding criterion is : " ' '•

.0, ... (3)O

i n which - ' - - . . . . . .

where

j upward gas flow, ft/sec 'O .

• • ' ' • . .•

p density of vapor& • ' ' • " • » •

g local gravity . . .

d horizontal spacing between tubessp, density of liquid

j downward liquid flow, ft/sec

In using this criterion, we assumed that at the holdup condition, no liquid condensate.*was dropping, or jf = 0.

RESULTS AND DISCUSSION

Twenty-four runs were made with the nitrogen prototype heat exchanger. The elec-trical heat input to simulate the gamma and neutron heating ranged from 500 to 6000watts. The design heat load for the nitrogen prototype was approximately 2400 watts.

A computer code was developed incorporating the correlations discussed in the lastsection. The output of the code was the heat extracted in the condensing process. Ta-ble I summarizes the principal operating conditions, including the calculated and meas-ured electrical heat to the apparatus. Generally, when the calculated and experimentalheat inputs are compared, they are in relatively good agreement. One can conclude thatthe design analysis is fairly accurate as long as steady-state operation takes place.There remains the question of flooding or holdup, which would make the condenser in-operative.

It was estimated by the analysis of reference 3 that the threshold of flooding wouldnot be encountered until heat rates 2,, times the design value were realized. The unusualgeometry of the heat exchanger quadrant did raise some doubts whether the floodingcriterion was meaningful. It was suggested that a kind of horizontal flow holdup couldoccur. This speculation meant that the condensate accumulated in the bottom of thesmaller diameter shell (fig. 1, right side of drawing) could be backed up by a counter-flow of the vapor. This situation could result in a flooding excursion and an inoperativecondenser. To test this idea, a clear plastic model of the apparatus was built, and thevapor flow was simulated by a series of air jets and the liquid flow by water jets. Overa wide range of conditions (gas and liquid flow rates) there was no evidence for the be-ginning of a holdup transient. The volumetric rates of the gas and liquid were compara-ble to the actual ones in the heat exchanger. From this test and from the analysis doneon estimating holdup, it is concluded that holdup is not a likely possibility.

As was mentioned in the section APPARATUS AND PROCEDURE, some difficultywas incurred with several of the thermocouples in the instrumented condenser tube.Only two of the internal centerline thermocouples remained operable throughout the en-tire testing program. However, from knowledge of the inlet and exit coolant tempera-tures it was possible to gain valuable information about the bulk temperature distribu-tion along the length of the instrumented tube.

Figure 3 shows these bulk temperature distributions for ranges of flow rates andheat fluxes. It is evident that the distributions are not linear, especially near the rearof the heat exchanger where the sump is located. However, if one did assume a lineardistribution of bulk temperatures between the inlet and exit stations, it would not be a

6

bad approximation and would yield fairly good overall results. Such an assumption wouldnot reveal that the rear section of the condenser above the sump is doing most of thecondensing, as would be anticipated from an examination of the geometry.

CONCLUSION

*The main conclusion from a design and performance evaluation is that a heat ex-

changer with a horizontal condenser bank can be designed by using standard heat-transfer correlations and that the condenser will operate stably without holdup over aconsiderable heating range. The condenser described in this report handled 4. 6 watts

2 1per square centimeter (30 W/in. ), which was approximately 2^ times its design ca-pacity.

Lewis Research Center,National Aeronautics and Space Administration,

Cleveland, Ohio, April 7, 1972,111-05.

REFERENCES

1. Simoneau, R. J.; and Hendricks, R. C.: A Simple Equation for Correlating Turbu-lent Heat Transfer to a Gas. Paper 64-HT-36, ASME, Aug. 1964.

2. Jakob, Max: Heat Transfer. Vol. 1. John Wiley & Sons, Inc., 1949.

3. Wallis, Graham: One-Dimensional Two-Phase Flow. McGraw-Hill Book Co.,Inc., 1969.

TABLE I. - SUMMARY OF NITROGEN-HEAT-EXCHANGER PERFORMANCE

Flow

m3/hr

'17.018.2

17.0

14.712.3

2. 5

2 .45.0

2.82.7

4.92.7

2.5

2.4 >" 2. 3 '

1. 11.03.5

3.5

3.4

2.7

gal/miri

74. 479. 8 -

74.4

64.454.0

11.0

10.4

21.912.5

12.0

21.7

11.6

10.910.610.2

5.0

4. 515.4

15.2

14.8

11.9

Chamber pressure

N/cm2

'12.0512.36

14.09

18.2921.77

29.94

59. 1445. 1429. 27

55.44

49.2328.47

43. 50

55.6472.39

42.6854.05

24.33

44.81

58.6727.64

Ib/in. 2 abs

17.48' ' 17.93;

20.44

26.53

31.58

43.43

85.7865.4842.46

80.41

71.4141.30

63. 10

80.70105.00

61.90

78.4035.3065.00

85. 1040. 10

Chamber satura-tion temperature

K

78. 9779 .20 '

80.39

82.89

84.68

88.01

97.96

92.6887.79

95.24

93.74

87.48-

92.2995. 4699.02

92.01

95.0785.79

92.68

96.0787. 18

• °R

142. 05142. 45

144.60

149. 10152.30

158.. 30

176.20166.70157.90

171.30

168.60

157. 35

166.00174. 70178. 10

165. 50

171.00154.30

166.70

172.80156.80

Heat, Q, W

Actual

5001000

2000

4000

4000

2500

50006000

2500

5500

60002500

4000

5000.6000

2500

30002500

5000

60002500

Calcu-

lated

445940

1825

35283612

2863

56076592

2933

5228

6771

2747

406849545791

2340

26072720

5238

63582733

^calculated ,', ^QQ

^actual ''

percent

' 8994

91

8890

115112110

117

95

113110

102

9997

94

87109

105

106109

-Condenser tubes

Discharge line (two)-

Fill line

Vacuum vessel '..

-VCoolant

Figure 1. - Schematic of apparatus.

^Platinumresistancethermometer(T2)

Vapor temperature • (/ ) Pressure gagethermocoupleT ^ '

^Condenser tubes

Discharge line (two)

-—Referencejunctionblock-

^Inside bulktemperaturethermocouple Fj|| ,,ne

Vacuum vessel

Figure 2. - Instrumentation of condenser tube.

- Platinumresistancethermometer

yCoolant

^Turbineflowmeter

.9

Flow,m3/hr (gal/min)

2.6 (11.6)(10.9)(15.4)(15.2)

2.53.53.5

Heat flux,W

2500400025005000

(a) High flow rates.

12

10

Flow,m^/hr (gal/min)

o 2.4 (10.6)

Heat flux,W

20 40 60 8Length of tube, cm

100 120

10 14 18 22Length of tube, in.

(b) Low flow rates.

26 30

Figure 3. - Nitrogen coolant temperature rise tube-in-shell cryogenic con-denser.

10 A-Langley, 1972 33 E -6868

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